Postgresql 動態(tài)統(tǒng)計某一列的某一值出現(xiàn)的次數(shù)實例
實例解析:
select to_char(log.date, 'yyyy-MM-dd HH24') as hour, log.exten, sum(case log.grade when '1' then 1 else 0 end) as "1", sum(case log.grade when '2' then 1 else 0 end) as "2", sum(case log.grade when '3' then 1 else 0 end) as "3", sum(case log.grade when '4' then 1 else 0 end) as "4", sum(case log.grade when '5' then 1 else 0 end) as "5", log.direction from iface_satisfaction_investigation as log where log.date >= '2017-08-03 00:00:00' and log.date < '2017-08-04 00:00:00' group by hour,log.exten,log.direction order by hour,log.exten,log.direction asc
to_char:用于查詢時間格式化,to_char(log.date, 'yyyy-MM-dd HH24'),大致的結(jié)果是:2017-08-03 13
sum():毫無疑問是用來計算總和的。
sum(case log.grade when '1' then 1 else 0 end) 是計算什么呢?
他的意思就是:
計算grade這個列的值為1的時候有多少行,后面的sum(……)就類推了。
其他的也沒有什么好講的了
補充:PostgreSQL常用的統(tǒng)計信息
我就廢話不多說了,大家還是直接看代碼吧~
/*計算表的空間大小*/ select oid,table_schema as "模式", table_name as "表名", row_estimate::bigint as "表中的行數(shù)(估計值)", pg_size_pretty(total_bytes) as "總大小", pg_size_pretty(table_bytes) as "表大小", pg_size_pretty(index_bytes) as "索引大小", pg_size_pretty(toast_bytes) as "toast表總大小" from ( select *, total_bytes-index_bytes-coalesce(toast_bytes,0) as table_bytes from ( select c.oid, nspname as table_schema, relname as table_name, c.reltuples as row_estimate, pg_total_relation_size(c.oid) as total_bytes, pg_indexes_size(c.oid) as index_bytes, pg_total_relation_size(reltoastrelid) as toast_bytes from pg_class c left join pg_namespace n on n.oid = c.relnamespace where relkind = 'r' ) t1 ) t2 order by 2,3; /*統(tǒng)計用戶表信息*/ select schemaname as "模式", relname as "表名", seq_scan as "順序掃描的次數(shù)", seq_tup_read as "順序掃描獲取活動行的數(shù)量", idx_scan as "索引掃描次數(shù)", idx_tup_fetch as "索引掃描獲取活動行的數(shù)量", n_tup_ins as "累計插入的行數(shù)", n_tup_upd as "累計更新的行數(shù)(包含HOT 更新的行)", n_tup_del as "累計刪除的行數(shù)", n_live_tup as "當(dāng)前活動行估計數(shù)量", n_dead_tup as "當(dāng)前死亡行的估計數(shù)量", n_mod_since_analyze as "最后一次分析后被修改的行估計數(shù)量", last_vacuum as "上次被手動清理的時間(不統(tǒng)計VACUUM FULL)", last_autovacuum as "上次自動清理的時間", last_analyze as "上次手動分析的時間", last_autoanalyze as "上次自動清理分析的時間", vacuum_count as "手動清理的次數(shù)", autovacuum_count as "自動清理的次數(shù)", analyze_count as "手動分析的次數(shù)", autoanalyze_count as "自動分析的次數(shù)", pg_size_pretty(pg_table_size(relid)) as "表大小(不包含索引)" from pg_stat_user_tables order by 1; /*統(tǒng)計用戶表IO信息*/ select schemaname as "模式", relname as "表名", heap_blks_read as "讀取的磁盤塊數(shù)量", heap_blks_hit as "緩沖區(qū)命中數(shù)量", idx_blks_read as "表上所有索引讀取的磁盤塊數(shù)", idx_blks_hit as "表上的所有索引緩沖區(qū)命中數(shù)量", toast_blks_read as "TOAST表(如果有)讀取的磁盤塊數(shù)", toast_blks_hit as "TOAST表(如果有)緩沖區(qū)命中數(shù)量", tidx_blks_read as "TOAST表索引(如果有)讀取的磁盤塊數(shù)", tidx_blks_hit as "TOAST表索引(如果有)緩沖區(qū)命中數(shù)量" from pg_statio_user_tables order by 1; /*統(tǒng)計用戶索引信息*/ select indexrelid, schemaname as "模式", relname as "索引所在的表名稱", indexrelname as "索引名稱", idx_scan as "索引掃描次數(shù)", idx_tup_read as "索引掃描返回的索引項數(shù)量", idx_tup_fetch as "簡單索引掃描獲取的活動行數(shù)量", pg_size_pretty(pg_relation_size(indexrelid)) as "索引大小" from pg_stat_user_indexes order by 1,2; /*追蹤函數(shù),需要打開track_functions參數(shù)(默認(rèn)關(guān)閉)*/ select * from pg_stat_user_functions;
以上為個人經(jīng)驗,希望能給大家一個參考,也希望大家多多支持腳本之家。如有錯誤或未考慮完全的地方,望不吝賜教。
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